Radio Shack Quick Printer II Reference Handbook

L 8 L 4
o 0 UPPER
o 1 MIDDLE
o LOWER
It
I
LEFT I RIGHT
I
I
T
4 SCAN LINES
~
DIRECTION OF SCAN
1
CHARACTER POSITION ;;;;;: 6 GRAPHIC CELLS
FIGURE 7. Rectangle and Graphic Cells
Z8 is the Graphics Generator. Actually, Z8 does
not generate anything. Rather, it steers the
ASCII addresses around to simulate a graphics
generator.
The input to Z8 is ASCII from Data
Latch
Z28, and the higher order line address
from Z12, L4 and L8. L4 and L8 can represent
any four numbers from 0 to 3. But since Z12
never goes to binary 12 (except for so short a
time we can ignore it), we will only be looking
for a binary number from 0 to 3. L8 and L4 are
used
to specify the vertical address of the six
graphic cells.
There are three vertical addresses:
00 defines the uppermost pair of cells, 01
defines the middle pair of cells, 10 defines the
lower pair. This is also shown in Figure 7.
The ASCII word, labeled LB0 through LB5,
determines if the graphics cell is ON (high) or
OFF (low). The position of one of these inputs
to Z8 determines which side of the center line
the cell is located. An input at pin 6 of Z8 speci-
fies a left
hand graphic cell. Input at pin 10 of
Z8 specifies a right hand graphics cell. Pin 5,
left; pin 11, right; pin 4, left; pin 12, right. For
example: Assume LB2 is high and all other LB
inputs to Z8 are low. LB2 comes into Z8 at pin
5. This pin is associated with a graphic cell loca-
tion on the left of the character position. There-
fore,
depending on the status of L8 and L4, LB2
will
turn on (light) one of the graphic cells on
the left of center line. If L3 and L4 are at logical
00, the upper left cell is turned on. If L3 and L4
are 01, the middle left cell will light.
As
you can see, Z8's function as a graphics
generator is to steer the ASCII bits around the
character rectangle. The vertical position of the
graphics in the cell is determined by the status
of L8 and L4. The two outputs from Z8 are
labeled
"left" and "right". This "dot" informa-
tion is applied to the Graphics Shift Register. It
is in shift register logic that data from RAM Z63
determines if graphics or alphanumerics will be
written in anyone character position.
37

Radio Shack Quick Printer II Specifications

General

Brand	Radio Shack
Model	Quick Printer II
Category	Desktop
Language	English